In recent years, the use of fiber-reinforced polymer composite materials has become more prevalent in industries such as aerospace and automotive. These composite materials exhibit high strength as well as corrosion resistant properties in harsh environment. In addition, their light-weight property is particularly advantageous when compared to similar parts constructed from metals.
Fiber-reinforced polymer composites have been traditionally made from prepregs, which are formed of fibres impregnated with a curable matrix resin, such as epoxy. The resin content in the prepreg is relatively high, typically 20%-50% by weight. Multiple plies of prepregs may be cut to size for laying up, then subsequently assembled and shaped in a molding tool. In the case where the prepreg cannot be easily adapted to the shape of the molding tool, heating may be applied to the prepregs in order to gradually deform it to the shape of the molding surface.
More recently, fiber-reinforced polymer composites are made by utilizing liquid molding processes that involve resin infusion technologies, which include Resin Transfer Molding (RTM), Liquid Resin Infusion (LRI), Vacuum Assisted Resin Transfer Molding (VARTM), Resin Infusion with Flexible Tooling (RIFT), Vacuum Assisted Resin Infusion (VARI), Resin Film Infusion (RFI), Controlled Atmospheric Pressure Resin Infusion (CAPRI), VAP (Vacuum Assisted Process), Single Line Injection (SLI) and Constant Pressure Infusion (CPI) amongst others. In a resin infusion process, dry bindered fibers are first arranged in a mold as a preform and then injected or infused directly in-situ with liquid matrix resin. The term “bindered” as used herein means that a binder has been applied. The preform typically consists of one or more layers (i.e., plies) of dry, fibrous material that are assembled in a stacking arrangement where typically a powder, veil or film binder is utilized to maintain the desired geometry prior to resin infusion. After resin infusion, the resin-infused preform is cured according to a curing cycle to provide a finished composite article. Resin infusion is used not only to manufacture small, complex-shaped parts but it is also now used to manufacture large parts of aircrafts such as the entire wing.
In resin infusion, the fabrication of the preform to be infused with resin is a critical element—the preform is in essence the structural part awaiting resin. Hand layup has typically been used in the past to create composite preforms with detailed geometries. However, this is considered a time consuming operation with high risk of part-to-part variation. Thus, there remains a need for improvements in the fabrication of dry fibrous preforms for subsequent resin infusion.